Monolayer longitudinal bias and sensor trackwidth definition for overlaid anisotropic and giant magnetoresistive heads

Abstract

A magnetoresistive (MR) head and a method are disclosed providing a longitudinal bias layer and conductor leads at end regions of sensor elements to form a sensor region between the end regions. A uniform longitudinal bias thin film layer is deposited overlaying the entirety of the upper MR sensor, and a uniform conductor thin film layer is deposited overlaying the entirety of the longitudinal bias thin film layer. A photoresist process is conducted over the conductor thin film layer to develop a mask of the end regions and to expose a central region between the end regions. A reactive-ion-etching process completely etches the conductor thin film layer in the exposed central region to expose the longitudinal bias layer in the central region, the photoresist mask is removed, and an ion milling process of the exposed longitudinal bias layer at the central region reduces the bias layer from a "bias" critical thickness to a "null" critical thickness to free the MR sensor elements, thereby forming a defined sensor region of the underlying MR sensor elements at the exposed longitudinal bias layer at the central region.

I claim: 
     
       1. A magnetoresistive sensor comprising: a plurality of thin film layers providing a magnetoresistive sensor layer; and   a thin film monolayer of magnetic bias material overlaying said magnetoresistive sensor layer and having end regions and a central region between said end regions, said end regions having a thickness greater than a bias critical thickness to comprise a bias layer, said bias critical thickness comprising the thickness required to maintain a longitudinal bias field, to establish a longitudinal bias of said magnetoresistive sensor layer, and said central region having a thickness less than a null critical thickness, said null critical thickness comprising the thickness below which said longitudinal bias field is substantially zero.   
     
     
       2. The magnetoresistive sensor of claim 1, additionally comprising: a conductor thin film layer overlaying said thin film monolayer of magnetic bias material only at said end regions.   
     
     
       3. The magnetoresistive sensor of claim 2, wherein said thin film monolayer of magnetic bias material comprises Ni--Mn. 
     
     
       4. The magnetoresistive sensor of claim 3, wherein said bias critical thickness of said thin film monolayer of Ni--Mn is substantially 25 nm and said null critical thickness is substantially 10 nm. 
     
     
       5. The magnetoresistive sensor of claim 2, wherein said conductor layer comprises conductive Ta. 
     
     
       6. The magnetoresistive sensor of claim 2, additionally comprising: a layer of SiO 2  overlaying the entirety of said conductor thin film layer.   
     
     
       7. The anisotropic magnetoresistive sensor of claim 1, additionally comprising: a conductor thin film layer overlaying said thin film monolayer of magnetic bias material only at said end regions.   
     
     
       8. The anisotropic magnetoresistive sensor of claim 7, wherein said at least one bias layer comprises: a soft adjacent layer;   a spacer layer overlaying said soft adjacent layer; and   said at least one magnetoresistive sensor layer overlies said spacer layer.   
     
     
       9. The anisotropic magnetoresistive sensor of claim 8, wherein said at least one magnetoresistive sensor layer comprises Ni--Fe, and said thin film monolayer of magnetic bias material comprises Ni--Mn. 
     
     
       10. The anisotropic magnetoresistive sensor of claim 9, wherein said bias critical thickness of said thin film monolayer of Ni--Mn is substantially 25 nm and said null critical thickness is substantially 10 nm. 
     
     
       11. The anisotropic magnetoresistive sensor of claim 10, additionally comprising: a thin film layer of NiO underlaying said soft adjacent layer to pin said soft adjacent layer transverse bias, said thin film layer of NiO overlying said substrate.   
     
     
       12. An anisotropic magnetoresistive sensor positioned on a substrate comprising: at least one bias layer on said substrate for providing a transverse bias;   at least one magnetoresistive sensor layer overlaying said bias layer; and   a thin film monolayer of magnetic bias material overlaying said at least one magnetoresistive sensor layer, said thin film monolayer having end regions and a central region between said end regions, said end regions having a thickness greater than a bias critical thickness to comprise a bias layer, said bias critical thickness comprising the thickness required to maintain a longitudinal bias field, to establish a longitudinal bias of said at least one magnetoresistive sensor layer, and said central region having a thickness less than a null critical thickness, said null critical thickness comprising the thickness below which said longitudinal bias field is substantially zero.   
     
     
       13. A giant magnetoresistive sensor positioned on a substrate comprising: at least one pinning layer on said substrate for providing a magnetic pinning;   a plurality of giant magnetoresistive sensor layers overlaying said pinning layer; and   a thin film monolayer of magnetic bias material overlaying said plurality of giant magnetoresistive sensor layers, said thin film monolayer having end regions and a central region between said end regions, said end regions having a thickness greater than a bias critical thickness to comprise a bias layer, said bias critical thickness comprising the thickness required to maintain a longitudinal bias field, to establish a longitudinal bias of one of said plurality of giant magnetoresistive sensor layers, and said central region having a thickness less than a null critical thickness, said null critical thickness comprising the thickness below which said longitudinal bias field is substantially zero.   
     
     
       14. The giant magnetoresistive sensor of claim 13, additionally comprising: a conductor thin film layer overlaying said thin film monolayer of magnetic bias material only at said end regions.   
     
     
       15. The giant magnetoresistive sensor of claim 14, wherein said plurality of giant magnetoresistive sensor layers comprise: a first giant magnetoresistive ferromagnetic layer on said pinning layer;   a giant magnetoresistive spacer layer overlaying said first giant magnetoresistive ferromagnetic layer; and   a second giant magnetoresistive ferromagnetic layer overlaying said giant magnetoresistive spacer layer.   
     
     
       16. The giant magnetoresistive sensor of claim 15, wherein said second giant magnetoresistive ferromagnetic layer comprises Ni--Fe, and said thin film monolayer of magnetic bias material comprises Ni--Mn. 
     
     
       17. The giant magnetoresistive sensor of claim 16, wherein said bias critical thickness of said thin film monolayer of Ni--Mn is substantially 25 nm and said null critical thickness is substantilly 10 nm. 
     
     
       18. The giant magnetoresistive sensor of claim 15, wherein said at least one pinning layer comprises a thin film layer of NiO. 
     
     
       19. A magnetic storage system comprising: a magnetic storage medium having a plurality of tracks for recording of data;   a magnetic transducer maintained in a closely spaced position relative to said magnetic storage medium during relative motion between said magnetic transducer and said magnetic storage medium, said magnetic transducer including a magnetoresistive sensor formed on a substrate comprising: a plurality of thin film layers providing a magnetoresistive sensor layer; and   a thin film monolayer of magnetic bias material overlaying said magnetoresistive sensor layer and having end regions and a central region between said end regions, said end regions having a thickness greater than a bias critical thickness to comprise a bias layer, said bias critical thickness comprising the thickness required to maintain a longitudinal bias field, to establish a longitudinal bias of said transverse biased magnetoresistive sensor layer, and said central region having a thickness less than a null critical thickness, said null critical thickness comprising the thickness below which said longitudinal bias field is substantially zero;     an actuator coupled to said magnetic transducer for moving said magnetic transducer to selected tracks on said magnetic storage medium; and   a detector coupled to said magnetoresistive sensor for detective resistance changes in said magnetoresistive sensor layer responsive to magnetic fields representative of data bits recorded in said magnetic storage medium intercepted by said magnetoresistive sensor.   
     
     
       20. The magnetic storage system of claim 19, additionally comprising: a conductor thin film layer overlaying said thin film monolayer of magnetic bias material only at said end regions.   
     
     
       21. The magnetic storage system of claim 20, wherein said thin film monolayer of magnetic bias material comprises Ni--Mn. 
     
     
       22. The magnetic storage system of claim 21, wherein said bias critical thickness of said thin film monolayer of Ni--Mn is substantially 25 nm and said null critical thickness is substantially 10 nm. 
     
     
       23. The magnetic storage system of claim 20, wherein said conductor layer comprises conductive Ta. 
     
     
       24. The magnetic storage system of claim 20, additionally comprising: a layer of SiO 2  overlaying the entirety of said conductor thin film layer.   
     
     
       25. The magnetic storage system of claim 20, wherein said magnetoresistive sensor comprises an anisotropic magnetoresistive sensor having at least one bias layer on said substrate for providing a transverse bias, and said at least one magnetoresistive sensor layer overlays said bias layer. 
     
     
       26. The magnetic storage system of claim 25, wherein said at least one bias layer comprises: a soft adjacent layer; and   a spacer layer overlaying said soft adjacent layer.   
     
     
       27. The magnetic storage system of claim 26, wherein said at least one magnetoresistive sensor layer comprises Ni--Fe, and said thin film monolayer of magnetic bias material comprises Ni--Mn. 
     
     
       28. The magnetic storage system of claim 27, wherein said bias critical thickness of said thin film monolayer of Ni--Mn is substantially 25 nm and said null critical thickness is substantially 10 nm. 
     
     
       29. The magnetic storage system of claim 20, wherein said magnetoresistive sensor comprises a giant magnetoresistive sensor having at least one pinning layer on said substrate for providing a magnetic pinning, and said at least one magnetoresistive sensor layer comprises a plurality of giant magnetoresistive sensor layers overlaying said pinning layer. 
     
     
       30. The giant magnetoresistive sensor of claim 29, wherein said plurality of giant magnetoresistive sensor layers comprise: a first giant magnetoresistive ferromagnetic layer on said pinning layer;   a giant magnetoresistive spacer layer overlaying said first giant magnetoresistive ferromagnetic layer; and   a second giant magnetoresistive ferromagnetic layer overlying said giant magnetoresistive spacer layer.   
     
     
       31. The giant magnetoresistive sensor of claim 30, wherein said second giant magnetoresistive ferromagnetic layer comprises Ni--Fe, and said thin film monolayer of magnetic bias material comprises Ni--Mn. 
     
     
       32. The giant magnetoresistive sensor of claim 31, wherein said bias critical thickness of said thin film monolayer of Ni--Mn is substantially 25 nm and said null critical thickness is substantially 10 nm.